This application incorporates by reference Taiwanese application Serial No. 089116185, Filed Aug. 11, 2000.
1. Field of the Invention
The invention relates in general to a structure of a coaxial via hole, and more particularly to a coaxial via hole, which can be applied as a capacitor or a resistor and has the function of signal shielding.
2. Description of the Related Art
The development and progress of the IC (Integrated Circuit) integration and fabrication and the advance of device package and circuit design is always aimed to be smaller and lighter.
Conventionally, capacitor is fixed on the circuit board by Surface Mounted Technique (SMT), as shown in FIG. 1. The capacitor 102 is fixed on the pad 104 and the pad 104 is fixed on the circuit board (not shown). Trace 106 connects the pad 104 and via 108 on the circuit board. However, capacitor 102 fixed by SMT occupies large surface area, which is against the aim of size shrinking.
Via capacitors within substrate is proposed, with the development of high dielectric constant material. A typical one is disclosed in a U.S. Pat. No. 5,055,966. FIG. 2A shows the structure of the via capacitor within the multi-layer substrate; FIG. 2B is the cross-sectional view of the structure in FIG. 2A; FIG. 2C is the equivalent circuit of the capacitor at multi-layer substrate. The circuit board contains substrates L1, L2, L3, L4 and L5. A via 203 is formed in the substrate L3 and the via 203 is filled with dielectric. The conductive trace 204 above the via 203, the conductive trace 206 below the via 203 and the via 203 itself together form a capacitor. The capacitance C thereof is a function of the thickness of the substrate L3, the diameter of the via 203 and the dielectric constant of the dielectric.
Referring to FIGS. 3A to 3C, another structure of the conventional inter-layer capacitor is disclosed in U.S. Pat. No. 5,972,231, which contains two conductive plates 302, 304 of polygonal shape on top and bottom of the substrate 306. The conductive plates 302, 304 are coupled to surrounding circuitry at the polygonal vertices through conductive traces 308, 310, respectively. The inter-layer capacitor can be further extended to be a capacitor between multi-layer substrates by using via holes.
The two conventional capacitors mentioned-above occupy smaller horizontal surface but more substrate layers. However, increasing number of substrate layer is not acceptable for some Printed Circuit Boards (PCBs) with high device density. Similar problems also occur in the resistor structure.
It is therefore an object of the invention to provide a coaxial via hole used in a carrier, includes an outer cylinder-shaped conductor, an inner cylinder-shaped conductor, and an insulating fill. The outer cylinder-shaped conductor extends along the first direction. The inner cylinder-shaped conductor is in the outer cylinder-shaped conductor and extends along the first direction. The insulating fill is between the outer cylinder-shaped conductor and the inner cylinder-shaped conductor. It is therefore another object of the invention to provide a method of manufacturing a coaxial via hole. First, the first hole is formed in a carrier. A process to make the first hole become conduct electricity is then performed to form an outer cylinder-shaped conductor on the interior of the first hole. Next, an insulating material is placed in the outer cylinder-shaped conductor to form an insulating fill. The second hole in the insulating fill is then formed. The second hole has a diameter smaller than the diameter of the first hole. Next, a process to make the second hole become conduct electricity is performed to form an inner cylinder-shaped conductor on the interior of the second hole.
It is therefore another object of the invention to provide a coaxial via hole used in a carrier. The coaxial via hole includes an outer cylinder-shaped conductor, an inner cylinder-shaped conductor and an electrical-resistant fill. The outer cylinder-shaped conductor extends along the first direction. The inner cylinder-shaped conductor is in the outer cylinder-shaped conductor and extends along the first direction. The electrical-resistant fill is between the outer cylinder-shaped conductor and the inner cylinder-shaped conductor.
It is therefore a further object of the invention to provide a method of manufacturing a coaxial via hole. First, the first hole is formed in a PCB. A process to set hole become conduct electricity is then performed to form an outer cylinder-shaped conductor on the interior of the first hole. Next, an electrical-resistant material is placed in the outer cylinder-shaped conductor to form an electrical-resistant fill. The second hole in the electrical-resistant fill is then formed. The second hole has a diameter smaller than the diameter of the first hole. Next, a process to set hole become conduct electricity is performed to form an inner cylinder-shaped conductor on the interior of the second hole.